This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Ultra-Low Bias Current Difet®
OPERATIONAL AMPLIFIER
FEATURES ULTRA-LOW BIAS CURRENT: 100fA max
LOW OFFSET: 2mV max
LOW DRIFT: 10µV/°C max
HIGH OPEN-LOOP GAIN: 94dB min
LOW NOISE: 15nV/√Hz at 10kHz
PLASTIC DIP AND SO PACKAGES
APPLICATIONS PHOTODETECTOR PREAMPS
CHROMATOGRAPHY
ELECTROMETER AMPLIFIERS
MASS SPECTROMETERS
pH PROBE AMPLIFIERS
ION GAGE MEASUREMENT
DESCRIPTIONThe OPA129 is an ultra-low bias current monolithicoperational amplifier offered in an 8-pin PDIP andSO-8 package. Using advanced geometrydielectrically-isolated FET (Difet®) inputs, this monolithicamplifier achieves a high performance level.
Difet fabrication eliminates isolation-junction leakagecurrent—the main contributor to input bias current withconventional monolithic FETs. This reducesinput bias current by a factor of 10 to 100. Very lowinput bias current can be achieved without resorting tosmall-geometry FETs or CMOS designs which cansuffer from much larger offset voltage, voltage noise,drift, and poor power-supply rejection.
The OPA129 special pinout eliminates leakage currentthat occurs with other op amps. Pins 1 and 4 have nointernal connection, allowing circuit board guard traces—even with the surface-mount package version.
OPA129 is available in 8-pin DIP and SO packages,specified for operation from –40°C to +85°C.
+In
Output
6
Noise-FreeCascode
7
5
V–
V+
30kΩ 30kΩ
–In
3
2
Simplified Circuit
8
Substrate
OPA129
OPA129
OPA129
SBOS026A – JANUARY 1994 – REVISED APRIL 2007
www.ti.com
PRODUCTION DATA information is current as of publication date.Products conform to specifications per the terms of Texas Instrumentsstandard warranty. Production processing does not necessarily includetesting of all parameters.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications ofTexas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Difet is a registered trademark of Texas Instruments.All other trademarks are the property of their respective owners.
OPA1292SBOS026Awww.ti.com
SPECIFICATIONSELECTRICALAt VS = ±15V and TA = +25°C, unless otherwise noted. Pin 8 connected to ground.
NOTES: (1) High-speed automated test.(2) Overload recovery is defined as the time required for the output to return from saturation to linear operation following the removal of a 50% inputoverdrive.
OPA129PB, UB OPA129P, U
PARAMETER CONDITION MIN TYP MAX MIN TYP MAX UNITS
INPUT BIAS CURRENT(1) VCM = 0V ±30 ±100 * ±250 fAvs Temperature Doubles every 10°C *
Power Supply Voltage ...................................................................... ±18VDifferential Input Voltage ............................................................ V– to V+Input Voltage Range .................................................................... V– to V+Storage Temperature Range ......................................... –40°C to +125°COperating Temperature Range ...................................... –40°C to +125°COutput Short Circuit Duration(1) .................................................................. ContinuousJunction Temperature (TJ) ............................................................ +150°C
ABSOLUTE MAXIMUM RATINGS
NOTE: (1) Short circuit may be to power supply common at +25°C ambient.
PACKAGE INFORMATION(1)
PRODUCT PACKAGE-LEAD PACKAGE DESIGNATOR
OPA129P DIP-8 POPA129PB DIP-8 POPA129U SO-8 DOPA129UB SO-8 D
NOTE: (1) For the most current package and ordering information, see thePackage Option Addendum at the end of this data sheet, or see the TI websiteat www.ti.com.
CONNECTION DIAGRAM
ELECTROSTATICDISCHARGE SENSITIVITY
Any integrated circuit can be damaged by ESD. TexasInstruments recommends that all integrated circuits behandled with appropriate precautions. Failure to ob-serve proper handling and installation procedures cancause damage.
ESD damage can range from subtle performance deg-radation to complete device failure. Precision inte-grated circuits may be more susceptible to damagebecause very small parametric changes could causethe device not to meet published specifications.
Top View DIP/SO
TYPICAL PERFORMANCE CURVESAt TA = +25°C, +15VDC, unless otherwise noted.
1
2
3
4
8
7
6
5
Substrate
V+
Output
V–
NC
–In
+In
NC
OPA
NC: No internal connection.
OPA1294SBOS026Awww.ti.com
0
Frequency (Hz)
FULL-POWER OUTPUT vs FREQUENCY
Out
put V
olta
ge (
VP
P)
10k 100k1k 1M
30
20
10
10
Frequency (Hz)
INPUT VOLTAGE NOISE SPECTRAL DENSITY
Vol
tage
Den
sity
(nV
/√H
z)
1 10 100 1k 10k 100k
1k
100
10
1
0.1
0.01
–15 –10 –5 5 10 15
Common-Mode Voltage (V)
BIAS AND OFFSET CURRENT vs INPUT COMMON-MODE VOLTAGE
Nor
mal
ized
Bia
s an
d O
ffset
Cur
rent
0
BIAS AND OFFSET CURRENT vs TEMPERATURE
Ambient Temperature (°C)
Bia
s an
d O
ffset
Cur
rent
(fA
)
100pA
10pA
1pA
100
10
1
–50 50 125–25 0 25 75 100
IB and IOS
1001 1M 10M1k 10k 100k10
COMMON-MODE REJECTION vs FREQUENCY
Frequency (Hz)
Com
mon
-Mod
e R
ejec
tion
(dB
)
140
120
100
80
60
40
20
0
COMMON-MODE REJECTION vs INPUT COMMON-MODE VOLTAGE
The OPA129 uses a non-standard pinout to achieve lowestpossible input bias current. The negative power supply isconnected to pin 5—see Figure 1. This is done to reduce theleakage current from the V- supply (pin 4 on conventionalop amps) to the op amp input terminals. With this newpinout, sensitive inputs are separated from both powersupply pins.
FIGURE 1. Offset Adjust Circuit.
OFFSET VOLTAGE TRIM
The OPA129 has no conventional offset trim connections.Pin 1, next to the critical inverting input, has no internalconnection. This eliminates a source of leakage current andallows guarding of the input terminals. Pin 1 and pin 4, nextto the two input pins, have no internal connection. Thisallows an optimized circuit board layout with guarding—seethe Circuit Board Layout section.
Due to its laser-trimmed input stage, most applications donot require external offset voltage trimming. If trimming isrequired, the circuit shown in Figure 1 can be used. Powersupply voltages are divided down, filtered and applied to thenon-inverting input. The circuit shown is sensitive to varia-tion in the supply voltages. Regulation can be added, ifneeded.
GUARDING AND SHIELDING
Ultra-low input bias current op amps require precautions toachieve best performance. Leakage current on the surface ofcircuit board can exceed the input bias current of the ampli-fier. For example, a circuit board resistance of 1012Ω froma power supply pin to an input pin produces a current of15pA—more than 100 times the input bias current of the opamp.
To minimize surface leakage, a guard trace should com-pletely surround the input terminals and other circuitryconnecting to the inputs of the op amp. The DIP packageshould have a guard trace on both sides of the circuit board.The guard ring should be driven by a circuit node equal inpotential to the op amp inputs—see Figure 2. The substrate,pin 8, should also be connected to the circuit board guard toassure that the amplifier is fully surrounded by the guardpotential. This minimizes leakage current and noise pick-up.
Careful shielding is required to reduce noise pickup. Shield-ing near feedback components may also help reduce noisepick-up.
Triboelectric effects (friction-generated charge) can be atroublesome source of errors. Vibration of the circuit board,input connectors and input cables can cause noise and drift.Make the assembly as rigid as possible. Attach cables toavoid motion and vibration. Special low noise or low leak-age cables may help reduce noise and leakage current. Keepall input connections as short possible. Surface-mount com-ponents may reduce circuit board size and allow a more rigidassembly.
OPA129 VOUT
VIN
RF
RIN 2
3
67
5V+
V–
0.1µF220Ω
470kΩ 470kΩV–
V+
OPA129 7SBOS026A www.ti.com
CIRCUIT BOARD LAYOUT
The OPA129 uses a new pinout for ultra low input biascurrent. Pin 1 and pin 4 have no internal connection. Thisallows ample circuit board space for a guard ring surround-ing the op amp input pins—even with the tiny SO-8 surface-mount package. Figure 3 shows suggested circuit boardlayouts. The guard ring should be connected to pin 8 (sub-strate) as shown. It should be driven by a circuit node equalin potential to the input terminals of the op amp—see Figure2 for common circuit configurations.
TESTING
Accurately testing the OPA129 is extremely difficult due toits high performance. Ordinary test equipment may not beable to resolve the amplifier’s extremely low bias current.
Inaccurate bias current measurements can be due to:
1. Test socket leakage.
2. Unclean package.
3. Humidity or dew point condensations.
4. Circuit contamination from fingerprints or anti-statictreatment chemicals.
5. Test ambient temperature.
6. Load power dissipation.
7. Mechanical stress.
8. Electrostatic and electromagnetic interference.
1 8
54
1 8
54
(A) DIP package
(B) SOIC package
V–
V0
V+
V–
V0
V+
Connect to proper circuitnode, depending on circuitconfiguration (see Figure 2).
Connect to proper circuitnode, depending on circuitconfiguration (see Figure 2).
OPA129UB ACTIVE SOIC D 8 75 Green (RoHS &no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
OPA129UB/2K5 ACTIVE SOIC D 8 2500 Green (RoHS &no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
OPA129UB/2K5E4 ACTIVE SOIC D 8 2500 Green (RoHS &no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
OPA129UBE4 ACTIVE SOIC D 8 75 Green (RoHS &no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
OPA129UBG4 ACTIVE SOIC D 8 75 Green (RoHS &no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
OPA129UE4 ACTIVE SOIC D 8 75 Green (RoHS &no Sb/Br)
CU NIPDAU Level-3-260C-168 HR
(1) The marketing status values are defined as follows:ACTIVE: Product device recommended for new designs.LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part ina new design.PREVIEW: Device has been announced but is not in production. Samples may or may not be available.OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please checkhttp://www.ti.com/productcontent for the latest availability information and additional product content details.TBD: The Pb-Free/Green conversion plan has not been defined.Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirementsfor all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be solderedat high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die andpackage, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHScompatible) as defined above.Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flameretardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak soldertemperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it isprovided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to theaccuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to takereasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis onincoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limitedinformation may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TIto Customer on an annual basis.
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and otherchanges to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latestissue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current andcomplete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of salesupplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s termsand conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessaryto support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarilyperformed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products andapplications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provideadequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, orother intellectual property right relating to any combination, machine, or process in which TI components or services are used. Informationpublished by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty orendorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of thethird party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alterationand is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altereddocumentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or servicevoids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirementsconcerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or supportthat may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards whichanticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might causeharm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the useof any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is tohelp enable customers to design and create their own end-product solutions that meet applicable functional safety standards andrequirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the partieshave executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use inmilitary/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI componentswhich have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal andregulatory requirements in connection with such use.
TI has specifically designated certain components which meet ISO/TS16949 requirements, mainly for automotive use. Components whichhave not been so designated are neither designed nor intended for automotive use; and TI will not be responsible for any failure of suchcomponents to meet such requirements.
Products Applications
Audio www.ti.com/audio Automotive and Transportation www.ti.com/automotive
Amplifiers amplifier.ti.com Communications and Telecom www.ti.com/communications
Data Converters dataconverter.ti.com Computers and Peripherals www.ti.com/computers